SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 265 
WHERE 
  cscart_products_categories.product_id IN (
    13012, 10759, 10760, 10761, 10762, 10763, 
    10764, 10765, 10766, 9874, 9875, 9887, 
    9879, 9796, 9942, 9943, 9941, 9944, 
    10813, 10814, 10815, 10816, 10817, 
    10818, 10819, 10820, 10821, 10822, 
    10823, 10824, 10825, 10826, 12969, 
    10144, 10145, 10146, 10147, 10148, 
    10149, 10150, 10151, 10152, 10293, 
    10294, 10295, 10724, 10725, 10343, 
    10345, 10346, 10347, 10348, 10349, 
    10350, 10351, 10352, 10353, 10354, 
    10355, 10356, 10357, 10358, 10359, 
    10360
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00086

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "pt"],
      "key": "pt",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 64,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (13012,10759,10760,10761,10762,10763,10764,10765,10766,9874,9875,9887,9879,9796,9942,9943,9941,9944,10813,10814,10815,10816,10817,10818,10819,10820,10821,10822,10823,10824,10825,10826,12969,10144,10145,10146,10147,10148,10149,10150,10151,10152,10293,10294,10295,10724,10725,10343,10345,10346,10347,10348,10349,10350,10351,10352,10353,10354,10355,10356,10357,10358,10359,10360)"
    },
    "table": {
      "table_name": "product_position_source",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "pt"],
      "key": "PRIMARY",
      "key_length": "6",
      "used_key_parts": ["category_id", "product_id"],
      "ref": [
        "const",
        "noframes_angrybeaver.cscart_products_categories.product_id"
      ],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "ref": ["noframes_angrybeaver.cscart_products_categories.category_id"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_categories.storefront_id in (0,1) and (cscart_categories.usergroup_ids = '' or find_in_set(0,cscart_categories.usergroup_ids) or find_in_set(1,cscart_categories.usergroup_ids)) and cscart_categories.`status` in ('A','H')"
    }
  }
}